Synthesis of soluble core cross-linked polystyrene star polymer by application of acrylate-nitrile oxide ‘click chemistry’ using metal-free reagents†
In the present work, we have established a novel and environmentally benign method, whereby a 1,3-dipolar cycloaddition reaction has been applied using a non-toxic reagent, iodosobenzenediacetate [PhI(OAc)2], instead of the conventional copper-based reagents for the development of star-branched polymers. Here we have demonstrated the synthesis of core cross-linked star (CCS) polymers via the formation of isoxazoline ring using ‘click reaction’ between acrylate functionalities in a polymer chain and in situ generated nitrile oxide groups from a cross-linker added externally. In the initial step, a well-defined styrenic block copolymer with acrylate-functionalized middle-block was synthesized by controlled radical polymerization (RAFT) using α,α′-xylyl-bis(dithiobenzoate) as a chain transfer agent using 4-vinyl benzyl chloride and styrene as comonomers. Thereafter, the chlorobenzyl groups were converted into acrylate by reaction with acrylic acid. In the following step, core cross-linked star (CCS) polymers were synthesized by reacting the above block copolymer and oxime-functionalized cross-linkers (bi- and tetra-functional) using PhI(OAc)2 ‘click chemistry’. Formation of CCS polymers was confirmed from NMR, FTIR, GPC and DLS studies.